Method of operating thermionic-discharge devices



Oct. 12 1926. 1,603,152

- s. RUBEN METHOD OF OPERATING THERMLONIC DISCHARGE DEVICES Filed April 5, 1923 INVENTOR Samuel 1?:16 :0

ATTOR EY Patented Oct. 12, 1926,

V v pummel mew You, n. Y. 1 -mnon or ornnarmefiannainomc-nrscmnon nnvrcna This invention relates toa means for maintaining thermionic discharge currentsv at constant values. Its pnnclpal ob ect IS to provide a simple, hlghl efliclent means 5 .for stabilizing thermionlc 'scharges w1th1n much closer limitslthan is now possible by any present employeddevice In the various devlces operative by discharge of thermionic currents, and espec1ally those in which the cathodes are brought to high temperature for em1ss 1on 1t is important-to maintain the thermiomc currents at a high degree of constancy, and, 1n some applications, toprevent overload ng due tovariations in the discharge conditlons. In

these devices two factors are normally vanable, namely, the emission element tem erature and the conditions in the path 0 discharge, such as the degree of vacuum or pressure. As the potential for dllVlllg the thermionic discharge through the space ls' usually above the saturation value, any normal variations thereof are negllglble 1n 7 effect. I

2 To maintain constant conditions of operation, it is therefore necessary to compensate for variations in only those two factors. Variation in space condltlons 1n the highly evacuated of apparatus 1s usually due to the liberation of gas from the parts within the container, which become heated by the kinetic energy of impact of the oathode dischar e. In that type, such for mstance, as t e X ray tube operating by a heated cathode filament as the source of electron emission slight as liberation causes reduction 1n the disc arge currentand in the resultant work or effect of the emission, that is, the X ray radiation. To obtain the best results, these conditions must be maintained at a constant value. In those thermionic discharge devices in which the pressure is not so low. excessive positive ionization overheats the cathode with a rapidly increasin eif'ect in the tube, soon destroyin the ament by the bombardment of t e positive ions.

Various means have been employed to stabilize the electron stream upon the anode. but they have been only partiallv successful because of lack of close and continuous adjustment, slowness of action and inapplicability for use with high potentials. .My-invention is not so limited. It consists broadl of an arrangement and connection of electrical apparatus by which an element ms.- Serial an. ezazoa.

having a high coeflicient of resistance m series with the'emission element of the t er-- 111101110 device to be controlled, and the re-,

sistance 'of which is directlycontrolled by the thermlonic discharge current to be controlled or stabilized, is employed, in turn,

ably an iron wire, formed so as to present a large radiation area, as m a coil, constituting the plate element in a thermionic discharge, or regulating device, is heated by the current supplying the heat energy for the cathode of the device to be controlled,

. also by impact 'of the electron stream from Its own cooperatingelectrode, the potential therefor being obtained from a high resistance element in series with the cathode of the device to be controlled.

. Due to its normally high tem lierature and large radiation area,'the plate e ment radiates heat at a high rate, and-its response in electrical resistance, to temperature changes, is very quick.

As the kinetic energy of impact of the thermionic discharge in the regulating device heats its iron anode and increases the resistance thereof, any variation in the thermionic discharge in the controlled device causes a variation in the tem erature of the anode of the regulating device, and by the eifect of that impact, its resistance. This causes a variation in the current flowing .therethrough and through the cathode of the controlled device, and therefore, in the thermionic discharge therefrom, and in turn, a variation in the thermionic discharge in the regulating device, with resultant effect upon the anode, and so on. The operation of the regulating-device consequently, compensates for such variations, and maintains the thermionic discharge in the controlled device at constant value.

It. was found that when this arrangement was applied to X ray tube control, due to the very rapid thermal radiation from the anode of the regulating device, the X ray tube current was maintained with no perceptible fluctuation, even when wide variations occurred in the supply current.

The principle of the invention can bestbe further explained in connection with a certain illustrative embodiment of the invention in connection with an X ray tube, as one type of thermionic discharge device, as

shown in the accompanying drawing ;'but it is to be understood that the invention is also applicable to other devices operating by thermionic discharges, such as rectifiers, radio generators, etc.

The drawing illustrates the arrangement and connection of an X ray tube operating by thermionic discharge, with the electrical apparatus by means of whlch its d scharge is stabilized.

Referring more partlcularly to the drawing, 1 represents t e X ray tube and 2, 2 and 3 respectively, the emission element, the focussing element and the anode. At 4 1s the regulating, or thermionic discharge'device, with cathode 5 and anode 6. At 7 isa variable resistance, and at 8, reslstance m series with cathode 2, to give the resistance drop of potential for operating theregulating device 4. At 9 and 10 respectively are the secondary elements of the heating circuits for cathodes 5 and 2, 11 being the primary, the current being supplie therefor at terminals 12, 13 bein the terminals for the high potential direct current for the necessary potential for X ray rad ation.

In operation, when a potentlal 1s a-pphed at terminals 12, cathode 2, in tube 1, and cathode 5, in regulating tube 4, are heated to electron emission temperature. Anode 6, of the regulating tube is heated by the heating current in series circuit with cathode 2, the amount through it controlled by 1ts resistance. A high voltage being applied to terminals 13, a-thermionic current discharges between the electrodes in tube 1, and, due to the potential drop across resistance 8, a thermionic current discharges between cathode 5 and anode 6, of the regulating tube. Anode 6, is also heated by the kinetic energy of the thermionic discharge impact upon 1t carried .by the difference of potential across the resistance 8. Current supplied to cathode 2, of tube 1, is reduced accordingly as the resistance of anode 6, increases. To establish the desired normal operating conditions resistance 7, is varied until that current is discharged through tube 1, and resistance element 7, is set at that point. If then the thermionic current in tube 1, is then reduced in operation, by reason of the liberation of gas, as described, the discharge from cathode 5, upon anode 6, is reduced, and, due to its high resistance, coeflicient, its temperature and resistance are decreased, thereby permitting an increase in the current heating cathode 2 until the normal current again discharges through it.

For certain applications resistance element, 8, can be omitted from the circuit, when the normal resistance drop of potential across the regulating tube itself is sufficient.

' What I claim is 1. The combination with a thermionic disconnected in series with the cathode of said first named device, and means for controlling the discharge from said cathode by the thermionic discharge in said second named device, in response to variations in the discharge from said cathode.

2. The combination with a thermionic dis-.

charge device, of another thermionic discharge device having an anode composed substantially of iron connected in series with the cathode of said first named device, and I means for controlling the dischar e from said cathode by the thermionic discharge in said second'named device, in response to'variations in the discharge from said cathode.

3. The combination with a thermionic discharge device, of another thermionic dis-- charge devicehaving an anode composed of a material of high coefiicient of resistance connected in series with the-cathode of said first named device, and means for controlling the resistance of said anode b variations of the thermionic discharge om its cooperating electrode upon the anode in said second named device, 1n response to variations in the thermionic discharge from said cathode.

4. The combination with an X ray tube, of a thermionic discharge device, with means for controlling the thermionic discharge of said X ray tube by the impact of the thermionic discharge in said thermionic discharge device, in response to variations in the thermionic discharge in said X ray tube.

5. The combination of an X ray tube with a thermionic discharge device with means for cont-rollin the current flowing throu h the cathode of said tube, by variations in t e resistance of the anode element of said device in response to the impact of the thermionic discharge from its cooperating electrode in response to variations in ;the thermionic discharge in said X ray tube.

6. The combination of an X ray tube with a thermionic discharge device having-its anode element connected in series with the cathode of said tube, and means for controlling the thermionic discharge from said cathode by the resistance of said anode controlled by the thermionic discharge from said cathode.

7. In combination, a thermionic device, with another thermionic device havin an anode connected in series with the cat ode element of said first named device, said anode having a coefiicient of resistance higher than the coeflicient of resistance of sald cathode, and the discharge from said cathode being variable by the thermionic discharge in said second named device, in response to variations in the discharge from said cathode.

8. An arrangement for stabilizing the discharge in a thermionic device which comprises, in electrical connection a thermionic device, a second thermionic device, said second mentioned 'device having its anode connected in series with the cathode of said first mentioned device,and having a higher 00- eflicient of resistance than the coefficient of resistance of said cathode, said anode and said cathode being connected in series with a source of heating energy, a source of heating energy in the circuit of said second mentioned device, means for varying the otential between the cooperating electrod es of tween said source of potential and the cathodeof said first nameddevice, and an electrical connection between both of said cathodes, so arranged that a variation in the plate potential of said first mentioned device produces a variation in the plate potential of said second mentioned device.

Signed at New York city in the county of New York and State of New York this 24th day of March A. D. 1923.

, SAMUEL RUBEN. 

